Clinton takes the support of nearly two-thirds, or 63 percent, of Democratic respondents in the new Public Policy Polling (PPP) survey, while second-place Vice President Biden takes 13 percent support. That's virtually unchanged from last month's poll of the field.

The Republican field has been largely static since PPP began polling on 2016, six months ago. Rubio has seen a slight, two-percentage-point decline in support, while Bush has seen his support increase by three percentage points. Paul, however, has seen his support double since then.

While Clinton leads Paul and Rubio by 10 points each, Christie takes 44 percent support to her 47 percent support, largely due to his strong appeal with independents — he takes more independent voters than Clinton, in this poll.

The poll was conducted at the beginning of a week when congressional scrutiny of the administration's handling of the attack on the U.S. Consulate in Benghazi increased. Many Republicans see Benghazi as a possible line of attack against former Secretary of State Clinton.

But Dean Debnam, president of PPP, said the poll indicated that scrutiny hadn't yet hurt her 2016 chances.

"Benghazi isn’t having much impact on Hillary Clinton’s viability in a potential 2016 campaign," Debnam said in the polling memo. “She continues to lead the Democratic field and the top Republican candidate possibilities."

The survey was conducted among 1,099 registered voters from May 6-9, and has a 3-point margin of error for the overall survey, 4 points for the Democratic portion and 3.5 points for the Republican portion.